Self-Healing Coating Based On Disulfide Bond

During the transportation,storage and sales of the product,it is inevitable that the accidental impact will cause damage and damage to the packaging.After the packaging is damaged,the original mechanical properties,barrier properties,etc.of the packaging material will be lost,so that the quality of the product cannot be Continue to be protected.The self-healing packaging material can repair the damage in real time when the damage occurs,so that the product package can recover a certain proportion of the original performance after the damage.It therefore makes sense for the application of self-healing materials on packaging,especially in high value products.The disulfide bond is a covalent bond that can undergo a reversible reaction at a lower temperature and without external stimuli.A disulfide bond can be introduced into the polyurethane material to prepare a room temperature self-healing material.However,due to the weak disulfide bond,there is a lack of mechanical properties,which is difficult to use in packaging.In this paper,the mechanical properties of disulfide-bonded polyurethane materials are enhanced by adding castor oil(CO)cross-linking agent,introducing two kinds of chain extenders containing disulfide bonds and preparing aqueous self-healing polyurethane.The self-healing polyurethane film with the best comprehensive performance was selected as the coating on the PE film to prepare the self-healing composite film.The main research contents and results are as follows:(1)Firstly,a diol PD containing a disulfide bond and a hydrazide bond is prepared,and a series of PD is used as a chain extender,and castor oil(CO)or trimethylolpropane(TMP)is used as a crosslinking agent to prepare a series of Polyurethane materials PPG-CO and PPG-TMP containing disulfide bonds.The experimental results show that the short-chain cross-linking agent TMP has a negative effect on the self-healing properties of PU under the same proportion.Both CO and TMP can increase the tensile strength of the self-healing polyurethane,but reduce the elongation at break.With the addition of cross-linking agent,the degree of internal cross-linking increased,and the R(Strength)and R(strain)of self-healing PU showed a downward trend,indicating that the addition of cross-linking agent would decrease the self-healing properties of the material.When the molar ratio of PPG to CO is 7:3,the tensile strength of the sample is 0.84 MPa,the PU(0)is increased by 95.35%,and the R(Strength)and R(strain)are 80.95% and 69.36%,respectively.That is,when CO is used instead of 30 mol% of the PPG soft segment,the overall performance of the prepared PPG-CO is optimal.(2)Using PD and bis(2-aminophenyl)disulfide(AD)as chain extender,two kinds of poly(urea-urethane)materials containing different disulfide bonds with different soft segments were prepared.-AD and PTMG-AD.The experimental results show that the mechanical properties of PTMG–AD are far superior to those of PPG–AD.With the increase of AD addition and the decrease of soft segment content,the tensile strength of PPG-AD and PTMG-AD both increased,the elongation at break showed a downward trend,and the self-healing performance of PPG-AD decreased,while PTMG-The self-healing properties of AD first increase and then disappear.When the molar ratio of PPG:PD:AD is 6:4.5:4,the overall performance of PPG-AD3 is the best,the tensile strength is 0.74 MPa,and R(Strength)and R(strain)are 89.19% and 88.67%,respectively..When the molar ratio of PTMG:PD:AD is 7:4.5:3,the overall performance of PTMG-AD2 is the best,the tensile strength is 7.26 MPa,and R(Strength)and R(strain)are 86.63% and 76.67%,respectively..(3)Introducing a hydrophilic segment DMPA and a 2-hydroxyethyl disulfide 50% aqueous solution(HD)as a chain extender to prepare a series of water-based polyurethane materials WPU-HD containing disulfide bonds.The results show that the self-healing effect of WPU-HD can be effectively improved by increasing the amount of HD added.With the increase of HD addition,the R(Strength)of WPU-HD is increased from the initial 16.64% to 94.62%,but at the same time The tensile strength drops rapidly from the initial 12.74 MPa to 0.93 MPa.When the molar ratio of PTMG:HD is 8:6,the overall performance of WPU-HD3 is the best,the tensile strength is 3.54 MPa,and R(Strength)and R(strain)are 83.90% and 71.51%,respectively.(4)Selecting the best comprehensive performance of PTMG-AD2 and WPU-HD3 as coating,and using PE film as substrate,two self-healing composite films AD-PE and HD-PE were prepared.The results showed that the surface modification of PE substrate by KH-550 increased the peel strength between PTMG-AD2 and PE film by 42.01%,reaching 1.190 N/cm.The peel strength between the WPU-HD3 and the PE film was increased by 33.66% to 1.092 N/cm.The average tensile strength of AD-PE was 10.423 MPa,and the average R(Strength)was 51.5%.The average tensile strength of HD-PE was 6.931 MPa,and the average R(Strength)was 51.6%.